Stock Assessment of Four Dominant Shark Bycatch Species in Bottom Trawl Fisheries in the Northern South China Sea

Round 1

Reviewer 1 Report

Dear authors,

thank you for addressing the requests pointed out in the previous version of the manuscript.

I have one modification:

Table 1, caption: change "scientist name" in "scientific name" as in Table 2.

Author Response

Thank you for your comment.

We have revised "scientist name" of Table 1 as "scientific name" as in Table 2.

Reviewer 2 Report

I understand and confirm your revisions.

Author Response

Thank you again for your useful comment, which significantly improved our manuscript.

Reviewer 3 Report

I attach a pdf file with my comments to your revisions

Comments for author File: Comments.pdf

Author Response

Thank you for your comments. Please check our response in the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear Authors,

Almost all necessary corrections have been made by the authors. It was not understood why only one species (S. laticaudus) were estimated  parameters for LBB (Table 4).
I think that the article is suitable for publication as it is.

Best Regards.

Author Response

Thank you for your useful comments, which significantly improved our manuscript.

The analysis of Table 4 is designed to understand if the estimations are sensitive to different size-class intervals using LBB method. We choose S. laticaudus as an example because its length ranges is wide, which from 200 mm to 700 mm. The results showed the estimated parameters were insensitive to different intervals. 

We have added the descriptions in the Materials and Methods section.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Dear Authors,

This paper addresses an important topic on the cartilaginous fish species about stock assessment. Also the introduction and the purpose of the research are well organized. The manuscript has been written successfully. There are almost no deficiency between the references and the references in the content of the manuscript. The discussion can be improved by comparing the results with previous studies about shark species living in the different areas. Deficiencies and corrections in the manuscript are shown in added pdf format.

Best Regards.

Comments for author File: Comments.pdf

Reviewer 2 Report

The objective of the work is very interesting, the situation of fishing for sharks and rays in China's waters is certainly very important and at the same time not well managed. 
The demand for shark fins in Asian markets has led to mass killing of sharks and certainly needs serious management.
At present the authors have little data to tackle a robust assessment of the status of this stocks and use data-poor fisheries management approaches which, however, are not clearly presented in the paper and there are no supporting graphs.
In attached the text with some comments e revision.

Comments for author File: Comments.pdf

Reviewer 3 Report

Sharks are vulnerable to catch pressure, but resource analysis has little been conducted. This paper is the result of a survey using research vessel data, and the value of the data is high.

This research utilizes LBB method for data-poor fisheries management. However, authors ignore the accuracy of the LBB. Looking at the actual data (Fig. 3), C.sarawakensis: Lc is appropriate, and only large individuals with a small sample size for estimating Z. A.platyrhynchus: only large individuals with a small sample size for estimating Z, with only 3 plots. S.brevirostris: Frequency variation is so large and model fitting accuracy is poor.

Beside that, Fig. 3, which is the most important in this article, is unclear and the explanation of the figure is insufficient.

The author argued the interval of body length composition, but this small sample sizes can not improve the accuracy.

81 LBB > LBB (length-based Bayesian biomass)

83 I can not understand the reason that the CPUE index cannot be accurately expressed.

195-197, Table 3 Significant figures are not in place。

201 Estimates ranging 0.86-1.90 do not differ little.

Table 2 Numb+ers > Numbers

Figure 3 What is the model? Legends and labels are invisible.

Reviewer 4 Report

The authors highlighted very well the importance of implementing effective management plans for elasmobranch species as intrinsically vulnerable species that must be protected. I am proud to see that the authors put much effort in reporting ALL the threats insisting on these beautiful and ecologically important animals. Nevertheless, I see some obstacles and incongruences here. Beside the english form that in my opinion must be improved, the authors did not specify how they taxonomically identified  the species. Cryptic species and body-shape conservationism play an important role in species misidentification, inserting a huge bias in the statistics (first among everything bycatch!!!). I would like to see this enormous issue to be well discussed and some suggestions to be implemented in future perspectives to boost management programs.

Second, the authors were able to collect eleven species from NSCS; since they stated the huge problem of data deficiency, why did they decide to analyse only four of them and leave seven species out? I would recommend to extend this in the MS. They could refer to the results obtained on few individuals as preliminary, but still it would be an important result!

Here are minor revisions:

Abstract

Line 12. Please change “and for most Chondrichthyes species globally there is no formal fishery resource assessment.” as “and for most Chondrichthyes species there is no formal fishery resource assessment at the global level.“

Line 13. Change from “statuses” to “status”

Lines 14-15. The authors wrote “that which more than 100 samples in coastal waters of the northern South China Sea.”. I think a verb is missing; do you mean “of which more than 100 samples were collected in coastal waters of the northern South China Sea.”? Please, clarify.

Line 18. Change “fished” to “collected”.

Keywords should not be the exact words reported in the title.

Introduction

Line 32. Change “downward” with “top-down”.

Lines 44-45. Modify “with estimates ranging 63–273 million sharks globally, annually” as “with global estimates ranging 63–273 million sharks annually”.

Line 47. Modify “compounding” with “exacerbating”.

Line 62. Modify “long-lived, slow growing,” in “long-lived and slow growing animals,”.

Lines 73-74. “or discussions mainly regarded protection and management strategies”.

Line 76. Change “accurate” with “punctual”.

Lines 79 and 89 and check throughout the manuscript. Switch to “poor-data fisheries”.

Materials and Methods

Line 101. Delete “trawl”.

Line 103. The authors say “sharks were identified to species”. What did you use? Field guides? Dichotomy keys? Please, be specific, since species assignment is the key for identification and management!!

Line 105. The authors stated “Those species for which more than 100 individuals 105 were retained were selected for LBB analysis”. Why not all of the specimens collected? In this way you are missing seven species! Is an enormous lack.

Discussion

Line 225. Delete “’ [“